Russian President Vladimir Putin (c.) gestures as he walks by US President Barack Obama at a group photo outside of the Konstantin Palace in St. Petersburg, Russia, on Friday. World leaders discussed Syria's civil war at the summit but appear no closer to agreeing on international military intervention to stop it.

But the meeting ended as it began, with all attention focused on the cold-war-like dynamics between Russia and the US over the gathering crisis in Syria. At the final press conference Friday, following a compilation of dry economic decisions, Mr. Putin sent journalists scrambling to their Twitter accounts when he suggested Russia may "help" Syria if the US attacks.

"Will we help Syria? We will. And we are already helping, we send arms, we cooperate in the economic sphere, we hope to expand our cooperation in the humanitarian sphere, which includes sending humanitarian aid to support those people – the civilians – who have found themselves in a very dire situation in this country," Putin said.

'Complex monitoring'

Experts say that probably doesn't mean a repeat of old cold war scenarios, when one superpower might have put its forces on alert, started arming missiles, and sending out other flashing-red signals to warn the other that it may be going too far.

"We do not live in that world anymore. There is only one superpower today, and Russia is not going to do anything major to help Syria if the US attacks it," says Sergei Strokan, a foreign affairs columnist with the liberal Moscow daily Kommersant.

"Putin is referring to long-standing military-technical cooperation between Russia and Syria, and he may find ways to step that up, even by sending S-300 anti-aircraft missiles," he says.

In a major interview this week, Putin said Russia has already sent "components" of the S-300, which is similar to the US Patriot system, but did not complete the deliveries in the interests of maintaining stability. That might change, he implied, if the US attacks Syria.

Russia has sent three warships, including the giant guided-missile cruiser Moskva, to bolster its existing naval squadron in the eastern Mediterranean over the past week. But the Russian flotilla is dwarfed by US forces in the region and, in any case, Russian military officials have insisted that the forces will only be involved in "complex monitoring" of whatever happens in the region.

'There is a vacuum'

Media reports suggest the lines of division over Syria only hardened during a lavish banquet at the czarist-era Peterhof palace Thursday night. Putin stuck to his insistence that there is no hard proof that Syrian strongman Bashar al-Assad used poison gas against his own people in a widely disputed Aug. 21 incident near Damascus, and any action taken in response will be an illegal "act of aggression" unless it is cleared with the UN Security Council – where Russia holds a veto.

Mr. Obama reportedly got strong backing for his insistence on limited military strikes against Mr. Assad's regime only from leaders of France, Turkey, Canada, and Britain. But even fewer nations appeared to be fully in Russia's corner: Basically only China, a fellow veto-holding member of the UN Security Council, is prepared to give the Assad regime the benefit of the doubt on its alleged use of poison gas.

"There's a difference between declining to take part in military action, and supporting Russia's view that nothing should be done to condemn Assad," says Mr. Stokan. "Russia is not leading world opinion here, no matter how our leaders try to spin it."

Putin and Mr. Obama met for about 20 minutes on the sidelines of the St. Petersburg summit Friday to discuss Syria, and the vague official press statements that followed that chat suggested only that their "differences remain" and that "talks will continue" between Foreign Minister Sergei Lavrov and Secretary of State John Kerry.

"There was really no sense to discuss Syria at this G20 meeting at all. The US president came with his mind made up and his intention to launch a military strike publicly declared. It is unthinkable that a US president would change his mind over an issue like that after talking to foreign leaders," says Fyodor Lukyanov, editor of Russia in Global Affairs, a leading Moscow foreign policy journal.

"There is every reason, however, for Obama to have felt uncomfortable. Unlike the political atmosphere around the war in Iraq a decade ago, today there is not a lot of outright resistance to the idea of the US striking Syria. But there is a vacuum," Mr. Lukyanov adds.

"Everyone is watching to see what the US will do, but few want to get involved. And it looks very much like Obama's personal failure. The sense I get is that the other leaders were looking at him and thinking, 'maybe you're right, maybe you're wrong, but we're not going to go along with you. And it's because of you,' Basically, they don't trust Obama. That's very unfortunate, but does look like the inescapable conclusion here."